The optional SMCWD_GET_TIMELEFT command can be used to detect if
the watchdog has already been started.
See the implementation in OP-TEE secure OS [1].

At probe time, check if the watchdog is already started and then
set WDOG_HW_RUNNING in the watchdog status. This will cause the
watchdog framework to ping the watchdog until a userspace watchdog
daemon takes over the control.

Link: https://github.com/OP-TEE/optee_os/commit/a7f2d4bd8632 [1]

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
---
 drivers/watchdog/arm_smc_wdt.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/arm_smc_wdt.c b/drivers/watchdog/arm_smc_wdt.c
index 8f3d0c3a005fb..bbba23ace7b85 100644
--- a/drivers/watchdog/arm_smc_wdt.c
+++ b/drivers/watchdog/arm_smc_wdt.c
@@ -46,6 +46,8 @@ static int smcwd_call(struct watchdog_device *wdd, enum smcwd_call call,
 		return -ENODEV;
 	if (res->a0 == PSCI_RET_INVALID_PARAMS)
 		return -EINVAL;
+	if (res->a0 == PSCI_RET_DISABLED)
+		return -ENODATA;
 	if (res->a0 != PSCI_RET_SUCCESS)
 		return -EIO;
 	return 0;
@@ -131,10 +133,19 @@ static int smcwd_probe(struct platform_device *pdev)
 
 	wdd->info = &smcwd_info;
 	/* get_timeleft is optional */
-	if (smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL))
-		wdd->ops = &smcwd_ops;
-	else
+	err = smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL);
+	switch (err) {
+	case 0:
+		set_bit(WDOG_HW_RUNNING, &wdd->status);
+		fallthrough;
+	case -ENODATA:
 		wdd->ops = &smcwd_timeleft_ops;
+		break;
+	default:
+		wdd->ops = &smcwd_ops;
+		break;
+	}
+
 	wdd->timeout = res.a2;
 	wdd->max_timeout = res.a2;
 	wdd->min_timeout = res.a1;

base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21
-- 
2.34.1

On 5/20/25 01:59, Antonio Borneo wrote:
> The optional SMCWD_GET_TIMELEFT command can be used to detect if
> the watchdog has already been started.
> See the implementation in OP-TEE secure OS [1].
> 
> At probe time, check if the watchdog is already started and then
> set WDOG_HW_RUNNING in the watchdog status. This will cause the
> watchdog framework to ping the watchdog until a userspace watchdog
> daemon takes over the control.
> 
> Link: https://github.com/OP-TEE/optee_os/commit/a7f2d4bd8632 [1]
> 
> Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>   drivers/watchdog/arm_smc_wdt.c | 17 ++++++++++++++---
>   1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/watchdog/arm_smc_wdt.c b/drivers/watchdog/arm_smc_wdt.c
> index 8f3d0c3a005fb..bbba23ace7b85 100644
> --- a/drivers/watchdog/arm_smc_wdt.c
> +++ b/drivers/watchdog/arm_smc_wdt.c
> @@ -46,6 +46,8 @@ static int smcwd_call(struct watchdog_device *wdd, enum smcwd_call call,
>   		return -ENODEV;
>   	if (res->a0 == PSCI_RET_INVALID_PARAMS)
>   		return -EINVAL;
> +	if (res->a0 == PSCI_RET_DISABLED)
> +		return -ENODATA;
>   	if (res->a0 != PSCI_RET_SUCCESS)
>   		return -EIO;
>   	return 0;
> @@ -131,10 +133,19 @@ static int smcwd_probe(struct platform_device *pdev)
>   
>   	wdd->info = &smcwd_info;
>   	/* get_timeleft is optional */
> -	if (smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL))
> -		wdd->ops = &smcwd_ops;
> -	else
> +	err = smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL);
> +	switch (err) {
> +	case 0:
> +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> +		fallthrough;
> +	case -ENODATA:
>   		wdd->ops = &smcwd_timeleft_ops;
> +		break;
> +	default:
> +		wdd->ops = &smcwd_ops;
> +		break;
> +	}
> +
>   	wdd->timeout = res.a2;
>   	wdd->max_timeout = res.a2;
>   	wdd->min_timeout = res.a1;
> 
> base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21